DIY / MUFFLER

Refreshing Your Silencer with Packing: How to Wrap Stainless Wool and Glass Wool

A silencer that has lost its quieting effect can be revived by repacking it. We cover why stainless wool and glass wool are combined, how to wrap them, and even how to remove the baffle from a reverse cone muffler.

What you'll learn in this article

The role of packing (stainless wool and glass wool)
The order for wrapping the two types of packing, and why
Ways you should never use packing
How to remove the baffle from a reverse cone muffler

Inside a silencer, packing material is wrapped around to reduce exhaust noise. This packing gradually wears away with use, and older silencers often have lost much of their quieting effect.

Based on the method used by one of our staff builders, we show how to refresh a silencer using Silencer Stainless Wool and Silencer Glass Wool.

01 Two types of packing

消音ステンレスウール（左）と消音グラスウール（右） — Silencer stainless wool (left) and silencer glass wool (right)

Both are packing materials that dampen sound pressure waves to add a quieting effect. They're used in the so-called silencer section of the muffler, and they also work in pipe-in silencers.

Using the popular reverse cone shorty muffler as an example, we explain a setup that uses both stainless wool and glass wool.

リバースコーンショーティマフラー — Reverse cone shorty muffler

02 How to wrap the packing

Remove the end and take out the baffle inside (how to remove it is shown later). Out of the box, it's wrapped in glass wool, with an overall length of about 30cm.
First, wrap the stainless wool. You'll use about 1 meter of it.
The stainless wool fully wrapped.
Wrap the glass wool over it, using about 30cm. Finally, wind the included stainless wire around it to secure it.

POINT

Holding it in place with tape or similar before wrapping with wire makes it easier to secure.

03 Why wrap the stainless wool first?

The part in contact with the exhaust is under constant, heavy force. Glass wool, made of light, fine glass fibers, gets blown away little by little there until it's gone. Once the packing is gone, the quieting effect drops sharply. That's why old silencers lose their effectiveness.

Stainless wool doesn't blow away easily, so wrapping it first on the inside protects the glass wool on the outside.

POINT

This doesn't apply to silencers that don't use packing, such as those with walls forming expansion chambers.

So why not use stainless wool for everything? That's possible too. But it has drawbacks: it adds weight and costs more. It also seems to change the frequency range that's quieted, which shows up as a change in the exhaust note.

04 What not to do

The basic rule is to use packing where the exhaust doesn't hit it directly. The common setup is a "straight-through design" with wool wrapped around a perforated pipe. If you stuff wool into the exhaust path, it will quiet things down by reducing the flow area, but glass wool in particular will be gone in no time.

Notes

Non-serviceable silencers and those with a different quieting design are more difficult to work on. Check the construction carefully before starting.

05 How to remove the baffle from a reverse cone muffler

The reverse cone shorty's baffle is a tight fit and hard to pull out. Here are the steps for removing and refitting it.

Mark the seam between the end cap and the body so you can put it back in its original orientation when reassembling. As a rule, mechanical parts should always be reassembled in the same orientation and position.
Remove the screws (3) that hold the end cap.
Remove the end cap. It's tight, so be careful.
What you see inside is the inner baffle. It's also firmly seated and won't come out easily by hand.
So get a long rod and stand it upright on the ground.
Slide the silencer body onto the rod and work it up and down to push the baffle out.
The removed baffle.